3458A Cal Results

[dr.diesel]

A while back I scored a couple 3458As dead on ebay, recapped/replaced all the NVRAMs, and did the R411 60C mod.  I did an initial cal utilizing my unknown eBay 731B and a 10K PWW I already had from Edwin, so the as-found is to be expected.  Both 3458As sat powered for several months before Cal once alive again.

Well last week it turns out I was headed directly past the cal lab that our friend @CalMachine works at, ENI labs in Fort Wayne IN.  I just picked everything back up yesterday and thought I'd share my experience and documentation provided by them.  I also included my 731B and asked them just to compare it to their 732B, no adjustment.

Overall the experience was great, ENI has a really nice facility and tons of equipment, which they are expanding.     ENI is also willing to accept DIYer gear, so if you have fancy homebrew reference and would like it compared to a known 732B, don't hesitate to contact @CalMachine.

Attached are the cal results, I need to further study how the uncertainty values are derived.

[lukier]

Thanks for sharing. Are you going to repeat these calibrations next year (to see the drift)?

A while back I scored a couple 3458As dead on ebay

Wow. Recently I was bidding on a "parts or repair unit" but I was outbid in the end - it went for $2600. IMHO that's too much for an untested unit (as it might have ADC drift or other expensive problems).
It seems it is very hard to get 3458A, even broken one, and then one must add duties, postage and possibly $1300-$2700 for Keysight parts or repair fee.

[dr.diesel]

Thanks for sharing. Are you going to repeat these calibrations next year (to see the drift)?

Yup, annual until I have a reasonable trend, then perhaps every 2 years.

[HighVoltage]

lukier
If you wait long enough, you can get lucky. In my case, I almost waited patiently for 2 years to find a good 3458A

dr.diesel
Thanks for sharing your cal docs.
Do you know what the real 10V value of the 732B was, when your 731B was tested?

[CalMachine]

Do you know what the real 10V value of the 732A was, when your 731B was tested?

The last transfer with Fluke resulted in a value of 9.9999615,  +/- 0.06ppm back in February.  The 732B is back in Fluke's possession for another transfer measurement.  Hopefully, I'll have it back in my hands again sometime next week!

[HighVoltage]

The last transfer with Fluke resulted in a value of 9.9999615,  +/- 0.06ppm back in February.  The 732B is back in Fluke's possession for another transfer measurement.  Hopefully, I'll have it back in my hands again sometime next week!

9.999,961,5 V for your 732B
9.999,803,0 V for D.Diesel' 731B

Not bad for this old 731B

Will your 732B ever be adjusted at the Fluke facility, like closer to 10V exactly or just kept at this value for tracing and comparison reasons?

[CalMachine]

The last transfer with Fluke resulted in a value of 9.9999615,  +/- 0.06ppm back in February.  The 732B is back in Fluke's possession for another transfer measurement.  Hopefully, I'll have it back in my hands again sometime next week!

9.999,961,5 V for your 732B
9.999,803,0 V for D.Diesel' 731B

Not bad for this old 731B

Will your 732B ever be adjusted at the Fluke facility, like closer to 10V exactly or just kept at this value for tracing and comparison reasons?

This unit will, most likely, never be adjusted.  With as many transfers as we've had on this in the past, we develop a linear regression model to better predict the unit's drift and true value over time. 

The only reason why I could see having our 732B adjusted to 10V nominal is if something were to happen to the unit to the point were its history is no longer applicable. 

[ManateeMafia]

Are the 731B measurements made over a period of several days or is it done in a single day?

I think some labs measure over several days but I don't know if they average the readings or if they test for stability and then take a final set of measurements on the last day.

[CalMachine]

Are the 731B measurements made over a period of several days or is it done in a single day?

I think some labs measure over several days but I don't know if they average the readings or if they test for stability and then take a final set of measurements on the last day.

I had let the 731B acclimate to the environment for a good 2 days.  I took multiple sets of 30 measurement samples every day, for 3 days.  Once I felt the mean and std deviation of the measurements were no longer dropping, and the reference had settled to the environment, I took the average of 3 30 measurement sets.

Improvements to my method are being made, as well! 

[Moon Winx]

There is an active debate of whether or not it's good to take several 732 measurements over several days or to take a single measurement the day it comes in and ship it right back out. The output of a 732 over time has a definite sinusoidal pattern laid over a linear drift line. The sinusoidal pattern is a pretty good match to seasonal relative humidity throughout the year. It has been observed that it takes about 40 days for the 732 to acclimate to the local humidity. So there is an argument that the best thing to do is calibrate it in place (these seasonal drifts can be predicted and corrected for), rather than send it anywhere. If you have to send it, get it back to within its environment as soon as possible.

[Moon Winx]

Also, I noticed you are performing these measurements at freezing temperatures. That must be one hell of an air conditioning system in your lab!

[Muxr]

Also, I noticed you are performing these measurements at freezing temperatures. That must be one hell of an air conditioning system in your lab!

hehe, -4 C ouch. That would be cold, below freezing.

[Tony_G]

Out of interest, why do the min, max numbers in the ENI report differ from that in a Keysight one?

For DC volt gain, Keysight:

1 V  min 0.99998942 max 1.00001024

For ENI:

1 V  min 0.99998900 max 1.00001100

Just wondering as I'm a calibration noob.

TonyG

[dr.diesel]

Also, I noticed you are performing these measurements at freezing temperatures. That must be one hell of an air conditioning system in your lab!

Swap F for C, that was actually fixed in the final documentation, sorry, forgot to note that above.

[Moon Winx]

Out of interest, why do the min, max numbers in the ENI report differ from that in a Keysight one?

For DC volt gain, Keysight:

1 V  min 0.99998942 max 1.00001024

For ENI:

1 V  min 0.99998900 max 1.00001100

Just wondering as I'm a calibration noob.

TonyG

I'm sure CalMachine can explain, but until then I'll butt in. Determining limits for a test point is a very complicated process and, in the end, is a mixture of science and art. There are proper universal ways to do this, but there are at least two steps in the accepted process that are completely determined by the lab: guardbanding technique and a subjective confidence coefficient for each component of the measurement uncertainty.

The guardbanding technique changes the test limits based on your measurement uncertainty, and the measurement uncertainty is calculated in real-time and takes into account the stability of the measurement, so it would actually be a red flag to me if you had constant test limits from test-to-test, let alone from lab-to-lab.

[Moon Winx]

...and another reason, the report states the test limits are stated at a 95% confidence level and perhaps Keysight states theirs at a different confidence level. Both sets of limits may be stated at different confidence levels but are actually describing the same data, or the same statistical distribution. Kind of like how you can swap between units degrees C and degrees F, but in the end you are describing the same temperature.

[CalMachine]

There is an active debate of whether or not it's good to take several 732 measurements over several days or to take a single measurement the day it comes in and ship it right back out. The output of a 732 over time has a definite sinusoidal pattern laid over a linear drift line. The sinusoidal pattern is a pretty good match to seasonal relative humidity throughout the year. It has been observed that it takes about 40 days for the 732 to acclimate to the local humidity. So there is an argument that the best thing to do is calibrate it in place (these seasonal drifts can be predicted and corrected for), rather than send it anywhere. If you have to send it, get it back to within its environment as soon as possible.

Noted!  I will look into this further, if possible.

Also, I noticed you are performing these measurements at freezing temperatures. That must be one hell of an air conditioning system in your lab!

 

What can I say...  I like it cold!   Lol!  Our software defaults to ºF and I had forgotten to change it to ºC.

Out of interest, why do the min, max numbers in the ENI report differ from that in a Keysight one?

For DC volt gain, Keysight:

1 V  min 0.99998942 max 1.00001024

For ENI:

1 V  min 0.99998900 max 1.00001100

Just wondering as I'm a calibration noob.

TonyG

Moon Winx explained it very well.   There could be a multitude of reasons why there are differing tolerances.  Confidence levels, Calibration Cycle, Guardbanding, even specific customer's needs.

TonyG were those tolerances stated on a traceable cal?  What's a little funny is, Keysight's stated tolerances are below that of the 3458A's stated specifications.  Interesting!  I'd like to know how they determined that

[Tony_G]

Yes they were. I purchased a 3458A at a great price and wanted to get it under a service contract. To do that it had to be calibrated so I sent it to their Loveland facility.

I have to say that they were absolutely fantastic to work with. Very impressed by them. I'd send you the cert PDF but I'm on vacation and the Keysight infoline site is down now.

TonyG

[PartialDischarge]

My unit arrived yesterday from ap. Attached are the cal results. Played a bit with the unit, after 3h warmup TEMP? reads 43,1º, but today is not that hot in Madrid.
This is what a 0.005% 10k vishay reads after ACAL DCV and ACAL OHM. Adrian told me that he will soon have his heated resistor standard calibrated with less that 1ppm uncertainty.
Will use the 3458 first to calibrate the 335A which is still very accurate but can do better, given that it was probably last calibrated 20 years ago.

[TiN]

What is the magic point in hiding 2823 in S/N number? It's all same for all US-made old HP 3458A's. 
Interesting calibration report, few things cought my eye:
* 90 day spec used as verification criteria. I'd rather expect 24 hour spec, however that is harder to reach for unknown history unit
* ANA mode for ACV instead of higher accuracy SYNC.
* AC HF calibration was not performed, based on equipment list.
* Giggle at using Rb for frequency check of 3458A.

As of 10K reading, that's likely not the true one. Execute OCOMP ON, DELAY 5, OHMF 10E3 , connect 4W, wait for hour or two, and then we see  . Yes, it's slow  .

Thanks for the work, MasterTech and Adrian  .

[Tony_G]

Yes they were. I purchased a 3458A at a great price and wanted to get it under a service contract. To do that it had to be calibrated so I sent it to their Loveland facility.

Here is the official doc from Keysight.

TonyG

[CalMachine]

Yes they were. I purchased a 3458A at a great price and wanted to get it under a service contract. To do that it had to be calibrated so I sent it to their Loveland facility.

Here is the official doc from Keysight.

TonyG

You're lucky!!  N6004465  Is their best metrologist they have.   

Thanks for the cert though.  I wonder what they do for an accredited cal.

[alm]

Yes they were. I purchased a 3458A at a great price and wanted to get it under a service contract. To do that it had to be calibrated so I sent it to their Loveland facility.

Here is the official doc from Keysight.

I assume, from the equipment list, that this is for the Keysight STE9000 'green checkmark' calibration, rather than the much more expensive calibration in their standards lab? Both are done at Loveland, but they do not offer the same performance (or price).

[Tony_G]

Yes, this is the basic Cal (no uncertainties, no guard banding, not in the standards lab). Price was around $600. I needed to do this to get it under the extended warranty but I also wanted to see how it changes from year to year so I'll do it again this year and see.

[alm]

Not sure if you can really rely on the data they provide to track drift. See these posts from the volt-nuts list for more detail about the calibration services. I am sure it will meet its specifications, but it sounds like they are only barely meeting the necessary test uncertainty ratio, so any inference beyond pass/fail is problematic.

[Tony_G]

Thanks - The statement that:

Knowing what I know, I'd rather send my 3458A for Standards Lab cal on a 3 year cal interval, instead of a one year cycle for STE9000 cal.

makes sense - I might do that as saving the one year cost for 3 years is roughly the Standard Lab Cost - I wasn't planning on having the unit calibrated every year but if I need to have the unit calibrated for the 3 year warranty then it might make sense to just save up each year and do the Standards Lab calibration and warranty extension at the same time.

[MisterDiodes]

Quick price update for anyone interested on Keysight 3458a service pricing - I just signed the invoice:

The extended warranty is $192 per year, and if the unit already has a current cal sticker, that will still qualify to start the warranty. If the meter is not under a valid cal period it will have to get cal'd first.

For me in Pacific Northwest USA, extended warranty contract also includes 1 free trip per year via courier service from either Seattle or Portland metro area to Rocklin, CA or Loveland, CO facilities for calibration.  Cal cost runs around $668 for standard, $1625 for high accuracy @ Loveland.  Otherwise you have to ship or drive the unit in yourself.

The warranty coverage is a very good deal, and if your business depends on a 3458a, it is highly recommended.  It helps you avoid those $2800 surprise repair bills.

If you have 732a/b's, I'd skip the expensive cal on the 3458a and keep the 732's on their cal schedule since those will get you in the much better 2ppm uncertainty range anyway for DCV.  732's start ~$575 per cal and that's a very good deal also.  Once your freshly cal'd 732's come in then you can keep your 3458a's checked against those.

[Tony_G]

Thanks for the info - Really appreciate it.

For me in Pacific Northwest USA, extended warranty contract also includes 1 free trip per year via courier service from either Seattle or Portland metro area to Rocklin, CA or Loveland, CO facilities for calibration.  Cal cost runs around $668 for standard, $1625 for high accuracy @ Loveland.  Otherwise you have to ship or drive the unit in yourself.

Where did you find this information? I have my unit, coincidently also in the PNW, under the 3 year warranty but I missed the bit about free shipping apparently 

Also do you know if they'll extend the warranty while under warranty but without a subsequent calibration? I ask because they want the cal to confirm the unit works but if it is already under warranty then any failures would be repaired anyway so why not extend it.

TonyG

[orin]

Thanks for the info - Really appreciate it.

For me in Pacific Northwest USA, extended warranty contract also includes 1 free trip per year via courier service from either Seattle or Portland metro area to Rocklin, CA or Loveland, CO facilities for calibration.  Cal cost runs around $668 for standard, $1625 for high accuracy @ Loveland.  Otherwise you have to ship or drive the unit in yourself.

Where did you find this information? I have my unit, coincidently also in the PNW, under the 3 year warranty but I missed the bit about free shipping apparently 

Also do you know if they'll extend the warranty while under warranty but without a subsequent calibration? I ask because they want the cal to confirm the unit works but if it is already under warranty then any failures would be repaired anyway so why not extend it.

TonyG

I don't see why not.

If it's anything like the 34461A, when I extended its warranty, they asked how many years I wanted quoted - up to 5 years.  I chose 3 and they gave a tiny discount for the multi-year contract.  They mustn't break very often as it was $36 a year.

However, if they have to repair a 3458A, they would likely have to recalibrate it as part of the repair.  I wonder how they handle that if you send it in for repair out of cal.

[ManateeMafia]

Mine failed last year under warranty. I haven't opened it to confirm but they said they replaced the A1 board. The 5 year contract was bought and paid for at that point.

Of note, the instrument returned with no detailed repair information. It just came back with the usual cal cert.

I have always paid for shipping to Keysight but they paid for return shipping. The return delivery gets marked hold for pickup (at my request) so it doesn't bounce around in the truck all day in the Florida heat.
If you call before shipping, they may tell you to ship to Rocklin. When I ask about Loveland, they tell me to ship it there instead.

[MisterDiodes]

Tony:

RE: Shipping - that's how it works for us, ask your sales rep.  Sometimes you do get conflicting info depending on who you call, some of the reps know, some don't.   Maybe you have to be near a Silicon Forest tech area where they are running courier service anyway.  I'm near I-5 corridor so maybe that why it works out.  I don't think they are going to drive 400 miles out in the sticks for one meter, but I'm not sure.  I'll ask next time I have occasion to talk to them.  But that is something they definitely offer us for the $192 yearly charge - you call to setup a cal date, and then they tell you what is a nearby date a courier could be scheduled with other errands in your area, and you go for that.  It might not be on the exact date you wanted, maybe +- a week or two, something like that.

Warranty - Actually our rep told us as long as it's working, you could even send it to a partner lab for cal (but she was a bit confused).  We just use KS.  I don't -think- there is a requirement to send it to KS for yearly cal, as long as it -stays- in cal with at least one of their cal partners.  I don't know that for sure but one of our clients does that, somehow:  They have the ext-warranty with KS but Transcat(?) does the yearly cal (just a basic cal of course, not the fancy-pants Loveland cal) - just because they have a contract with a local TransCat for a bunch of equipment anyway.  Somehow that all works out for everybody.

[Tony_G]

Thanks - they actually didn't mention it needing to stay in cal at all to me. Just that it had to be in cal to start the warranty. I'll have to contact them again.

TonyG

[MisterDiodes]

That sounds like KS sales...every time I call I get some slightly different story.  I guess everyone has to "compare notes" to get the whole picture.

[ap]

With regard to the KS cal report attached above, it is a little surprising that the 5720 used is specified for calibration on a yearly basis. That means a pretty bad test uncertainty ratio. I think I saw a similar one with a KS asia report. Anyone has some further insights?

[orin]

With regard to the KS cal report attached above, it is a little surprising that the 5720 used is specified for calibration on a yearly basis. That means a pretty bad test uncertainty ratio. I think I saw a similar one with a KS asia report. Anyone has some further insights?

Given these notes on the cal report:

"The Input value under TEST CONDITIONS column is the nominal value applied.
The MINIMUM and MAXIMUM test limits are based on the actual value applied
that is expected to be the indicated (MEASURED) value.
This can be calculated from:
Expected Value=(Minimum+Maximum)/2"

I'd expect that the 3458A in the calibration standards used section is used to measure the actual 5720A output and generate the limits.  This 3458A would no doubt be very well characterized and on a very short cal cycle.

[ap]

Thats probably how they do it, so that the 5720 is used as a source only. I actually overlooked this. Still not that great in some cases, but anyway. Would also be in line with the standard cal procedure.

[alm]

If you read the link I posted earlier with information from the engineer who designed the procedure, that is exactly what they do. The 3458a is on a 90 day cycle and is well characterized. The calibrator acts as a stable source and only its 15 min stability counts towards the measurement uncertainty. But TUR is indeed borderline.

[MisterDiodes]

If your interested mainly in lowest uncertainty on DCV and resistance, we don't consider the Loveland cal service the best value.  Over long term, money is better spent keeping some cal'd 732's (and KVD's + 752) right next to the stack of 3458a's, and right next to 732's you keep an SR-1010 for resistance checks.  The SR-1010 is easily much more stable over time than any 3458a and can be counted on as an excellent Rref.

Now you can keep your 3458a fleet tuned up and locked on to ~2ppm uncertainty DCV and check them any time for drift - and just send them out for standard cal as required if you need ACV, amps etc. or if you're doing an ISO900x audit and need outside verification.  That's probably as good or better than Loveland will get you for DCV anyway.

If you count the risk of bouncing that meter along in a truck on the trip to and from Loveland, keeping the 732's cal'd generally will get you a better result for lower uncertainty at the same or less cost over time, and at much less risk.